Bahamut
Bahamut was originally a Celestial in Heaven. When the Source sought volunteers to descend to the Midplane to stop the Devils from destroying Creation, Bahamut was among those who went. Observing the dragon-like demons present in the Midplane, he based his form off of them, manifesting as a majestic platinum dragon. However, shortly afterward he assumed a more humanoid shape for ease of interacting with other material beings (though this humanoid shape was of massive size compared to those assumed by the others). Followed by dozens of Gods (as these incarnated Celestials called themselves), Bahamut lead them in battle against the Devils to restore order to the Midplane. The Devils were stronger than many of the Gods, requiring Bahamut to break his followers into parties who would take out the Demon Lords one by one rather than all at once. The tendency against teamwork of the Devils aided the gods in their mission. He observed with worry Adam's relationship with Lilith, and was heartbroken when she fell in with the devils and betrayed the Gods. By now Satan had become aware of the Gods and was hunting them down looking for a worthy opponent. Believing he was the only one who stood a chance against him, Bahamut lead a final expedition into Hell to take out Satan once and for all. The group encountered Lilith, and Adam stayed behind to fight her while Bahamut and Marduk continued on to find Satan. When they found him, the Devil King quickly killed Marduk, and Bahamut engaged him in battle. The two seemed roughly even until Bahamut noticed that Satan was drawing out the fight for his own amusement. When Adam arrived Bahamut managed to destroy Satan's body, and in the time before he regenerated he implanted his power into Adam. As Satan managed to reconstitute his body, Bahamut shifted into his dragon form and grabbing Satan, dove into the icy river Cocytus at the bottom of Hell. He used the last of his energy to turn his body into a prison of ice from which Satan could never escape. Adam went on to raise the barrier between the planes, ensuring the success of Bahamut's plans. Before incarnating as a God, Bahamut was among the greatest of Celestials, rivaling even Lucifer before his fall. What few know is that Bahamut did not begin life as a Celestial, but was a mortal aesthetic from Earth who achieved enlightenment. Upon ascending to Heaven, he stretched his consciousness across all of time and space and was therefore present at the beginning when Creation occurred. 'Powers and Abilities' 'Thunder Dragon' Upon his emergence in the Midplane, one of Bahamut's first actions was to infuse himself with and master the Element of Thunder. The Element vastly increased his already substantial power, allowing him to fight toe to toe with Satan. Before his death he would pass his power to his lieutenant, Adam. 'Trivia' - Despite having been a Celestial who participated in the Act of Creation, he was not a Celestial who emerged in the Dreaming which proceeded it. Instead, Bahamut was originally a human sage on Earth who achieved enlightenment. Upon becoming ethereal, he was able to stretch himself over all of space and time, and was therefore present at the beginning of the Universe.